Has your hydrometer been calibrated in distilled water? Are you reading the bottom of the meniscus? I'll assume that the answers to these questions is "yes" so we can eliminate equipment error from the readings. I'm not trying to be insulting, just establishing a baseline for your readings.
It seems that you're getting more fermentability from your mash and/or attenuation from your yeast.
In the Starter tab, you can adjust the yeast's max attenuation to match your results. A pretty simple fix that assumes you use the same yeast and the same pitching rates.
Temperatures warmer than optimal for the yeast can increase apparent attenuation. Are your fermentation temperatures optimal, stable and repeatable?
Longer mash times can yield more fermentable worts. If you have extended mash times or sparges that don't hit mashout, this could be a factor. In the Options > Advanced tab, you can change the mash attenuation slope and where the knee is. If your increased attenuation is found across a range of yeasts and worts, then this adjustment is your best bet.